Log a warning if custom DefaultCookieSerializer does not have rememberMeRequestAttribute set

Closes gh-2568

spring-session-core/src/main/java/org/springframework/session/config/annotation/web/http/SpringHttpSessionConfiguration.java

@@ -108,9 +108,7 @@ public class SpringHttpSessionConfiguration implements InitializingBean, Applica
 
 	@Override
 	public void afterPropertiesSet() {
-		CookieSerializer cookieSerializer = (this.cookieSerializer != null) ? this.cookieSerializer
-				: createDefaultCookieSerializer();
-		this.defaultHttpSessionIdResolver.setCookieSerializer(cookieSerializer);
+		this.defaultHttpSessionIdResolver.setCookieSerializer(getCookieSerializer());
 	}
 
 	@Bean
@@ -154,6 +152,21 @@ public class SpringHttpSessionConfiguration implements InitializingBean, Applica
 		this.httpSessionListeners = listeners;
 	}
 
+	private CookieSerializer getCookieSerializer() {
+		if (this.cookieSerializer != null) {
+			if (this.cookieSerializer instanceof DefaultCookieSerializer defaultCookieSerializer
+					&& this.usesSpringSessionRememberMeServices
+					&& defaultCookieSerializer.getRememberMeRequestAttribute() == null) {
+				this.logger.warn("Spring Session Remember Me support is enabled "
+						+ "and the DefaultCookieSerializer is provided explicitly. "
+						+ "The DefaultCookieSerializer must be configured with "
+						+ "setRememberMeRequestAttribute(String) in order to support Remember Me.");
+			}
+			return this.cookieSerializer;
+		}
+		return createDefaultCookieSerializer();
+	}
+
 	private CookieSerializer createDefaultCookieSerializer() {
 		DefaultCookieSerializer cookieSerializer = new DefaultCookieSerializer();
 		if (this.servletContext != null) {

spring-session-core/src/main/java/org/springframework/session/web/http/DefaultCookieSerializer.java

@@ -434,4 +434,14 @@ public class DefaultCookieSerializer implements CookieSerializer {
 		return this.cookiePath;
 	}
 
+	/**
+	 * Gets the name of the request attribute that is checked to see if the cookie should
+	 * be written with {@link Integer#MAX_VALUE}.
+	 * @return the remember me request attribute
+	 * @since 3.2
+	 */
+	public String getRememberMeRequestAttribute() {
+		return this.rememberMeRequestAttribute;
+	}
+
 }